Everyone is different, I had the same mentality last semester in my organic class but the thing is I have really bad ADD that I can't read a damn textbook.
The best way to learn, for me, is to have someone explain it to me, once I understand it, it clicks and that's that.
I think it's a waste of time (for me) to read and reread something over and over when I could utilize something as great as the tutoring center on campus, some might say this is lazy however this is very efficient for me.
What I then do after I learn the material is go through the textbook and do practice problems and anything I don't have down 110% completely I go back to the tutoring place.
For the upper division classes that might not offer tutoring I suggest you just befriend the professor and go to his office hours. Even if you don't have much to ask him just go and sit there and do your work and questions will come up guaranteed. I'm sure the professor won't mind and he'll take an appreciation to the fact that you're trying to learn.
I hate the word studying btw, because it suggests that you're perched over a book in the library for hours at a time. Just try to actually LEARN the material, and the rest will follow.
Seriously I know your question is about A's but all an A is really isn't that you know 90% of the material, it simply is you putting more effort than 70% or 80% of the class (usually 10-30% gets awarded an A).
If you put effort you will see results its as simple as that. I've gotten several B's, but usually it's my fault, i just didn't try or I learned enough to get by.
Oh and also, don't compare yourself to the other people in your class, I met this kid in my organic class who told me what his study schedule is like (he said he studied only 3 days before the test and reviewed here and there) I had a tough time in the beginning so I asked him for advice... turns out this &*($#( was studying day and night, he had no social life what so ever, and here I was wondering why he was doing better than me.
Also, if your area offers a tutoring service that's outside the school and costs money, look into that. I have something like that here and I pretty much gave up on going to the huge class size and decided to attend those, they summarize the chapters for you and TEACH you the material, but they cost like $50-$75 a month, which is a small price to pay in the grand scheme of things imo.